Measurement of x-ray bremsstrahlung radiation from high energy electrons by stochastic acceleration in Heliotron J.

This article focuses on measuring and analyzing the electron energy distribution in stochastic acceleration experiments conducted in Heliotron J, a medium-sized heliotron-type magnetic confinement device. Using LaBr3(Ce) scintillators positioned around the device, x-ray bremsstrahlung radiation emitted by accelerated electrons was measured, and a Monte Carlo radiation transport simulation (PHITS code) was employed to account for the complex shielding effects of the vacuum vessel and coils. The results reveal that the electron energy distribution inside the vacuum vessel exhibits a Maxwellian shape below 450 keV and a power-law distribution above this energy, consistent with stochastic acceleration characteristics. Differences in electron flux between clockwise and counterclockwise directions were attributed to variations in initial electron populations produced by the toroidal electric field during the current ramp-up phase. The study outlines plans for improved temporal and spatial resolution in future measurements to further clarify the acceleration mechanisms.